For years, manufacturers have produced special containers for transporting and storing substrates and semiconductor wafers, and the like. Due to the delicate nature of the wafers and their extreme value, it is vital that they are properly protected throughout the transportation process. Since the handling of wafers is generally automated, it is necessary for wafers to be precisely positioned relative to the handling equipment for the robotic removal and insertion.
In addition to protection from damage by breakage, always in shipping storing or processing semiconductor wafers, cleanliness and contamination control is critical. The components and materials utilized must be very clean in the sense of not shedding or minimal shedding of particles and not exuding contaminants, such as gases, that can form film layers on the wafers. The containers and components are typically reused and must be amenable to cleaning and must be able to withstand repeated washing and drying cycles. Additionally, it is also critical, due to the commodity nature of wafer containers, particularly shippers for 100 mm and 150 mm wafers, that the containers are inexpensively manufactured and inexpensively maintained, such as replacement of component parts.
Conventional wafer shippers, particularly for 100 mm and 150 mm wafers comprise a wafer cassette, which holds a plurality of semiconductor wafers, contained in a wafer cassette container. The combination protects the wafers from mechanical damage and contamination during the storage and transportation. See for example, U.S. Pat. Nos. 4,949,848; 4,966,284; 4,793,488; and 5,273,159 for exemplary prior art wafer shippers. These patents are owned by the owner of the instant invention and are incorporated by reference herein.
The conventional wafer cassette is a single molded part generally comprising a front end having an H-bar machine interface portion, a back end having a panel, and sidewalls having slots comprising lower curved or converging portions following the curvature of the wafers, and with an open top and open bottom such as the device disclosed in U.S. Pat. No. 5,782,362 hereby fully incorporated herein by reference.
See element no. 1 in FIG. 12 of said reference. Also see U.S. Pat. No. 4,949,848 owned by the owner of the instant invention. The open bottom of such cassettes are defined by the side walls that extend downwardly from the converging portions in a parallel and vertical arrangement, and by the feet that extend downward from the sidewalls. The feet are generally planar, parallel, and with parallel edge surfaces upon which the carrier rests when it is seated with the open top upward. The edge surfaces will typically have an industry standard locating notch for engaging with a cooperating rib on a seating surface for proper positioning and forward rearward securement.
Such conventional cassettes generally have standardized dimensions, features, and configurations so as to be relatively interchangeable and useable with robotic processing equipment from a variety of manufacturers. This includes the H-bar and the parallel elongate feet with the notches. Additionally, for example, the “pitch”, or distance between the same surface of wafers stored in adjacent slots, is typically 0.1875 inch, while the depth of the slot at each sidewall is typically 0.440 inch.
The wafer cassette container or container portion of the shipper includes a lower base portion and a separate top cover portion having cushioning features for protecting the wafers during shipment. Some shippers, designed typically for 200 mm wafers or larger, include a bottom cushion secured to the base portion, see U.S. Pat. No. 5,273,159, for example. The cassette may conventionally be loaded robotically using the cassette oriented such that the H-bar side is positioned at the bottom of the cassette. The H-bar then functions as a machine interface to properly seat the cassette on an equipment surface so that wafers may be robotically inserted with the wafers in a horizontal plane into the open front of the cassette. The loaded cassette is then rotated 90 degrees such that the wafers are in a vertical plane and the loaded cassette is placed into the lower base portion of the wafer carrier container. Such conventional wafer carrier containers may have a location ribs in the bottom at a seating surface to cooperate with the locating notches on one or both of the feet to properly orient and seat the cassette.
Recently, the semiconductor industry has begun using wafers having a very thin cross sectional dimension. The thickness of these thin silicon wafers can be as thin as 200 um, in contrast with a typical conventional SEMI standard wafer thickness. Also, a thin germanium wafer thickness can be 125 um. Thin wafers present unique design considerations, and cassette style shippers are unsatisfactory in several respects for use with the thinner wafers. Thin wafers can be considered any wafer thickness that is less than the SEMI standard nominal thickness for wafers which is shown in the following table.
Wafer Standard DiameterWafer Standard Thickness100 mm525 um125 mm625 um150 mm675 um200 mm725 um300 mm775 um450 mm925 um
Another characteristic of thin wafers is that they can be substantially more fragile and prone to physical damage than a standard wafer. A conventional wafer carrier having limited support for the wafer around the extreme periphery of the wafer, causes increased stresses during shock events. The stress created makes the wafer even more prone to physical damage from shock or vibration.
The edges of thin wafers can be very sharp, and are formed from very hard materials, like silicon and germanium. These sharp edges can get caught on the cushion when the cover is installed causing cross-slotting and potentially causing damage to the wafer. Additionally, thin wafers may cut through softer materials that come into contact with the peripheral edge of the wafer, for example the wafer carrier plastic material.
Although existing containers are designed to reduce the effects of physical shock which can damage thin and fragile wafers, wafer containers are needed with improved shock reducing properties. There is a need for a wafer carrier specifically designed to be suitable for use with very thin wafers, in particular to accommodate their increased fragility while maintaining low manufacturing cost.